Class: Rails::Railtie

Overview

Railtie is the core of the Rails framework and provides several hooks to
extend Rails and/or modify the initialization process.

Every major component of Rails (Action Mailer, Action Controller, Action
View, Active Record and Active Resource) is a Railtie. Each of them is
responsible for their own initialization. This makes Rails itself absent of
any component hooks, allowing other components to be used in place of any
of the Rails defaults.

Developing a Rails extension does not require any implementation
of Railtie, but if you need to interact with the Rails framework during or
after boot, then Railtie is needed.

For example, an extension doing any of the following would require Railtie:

creating initializers

configuring a Rails framework for the application, like setting a generator

adding config.* keys to the environment

setting up a subscriber with ActiveSupport::Notifications

adding rake tasks

Creating your Railtie

To extend Rails using Railtie, create a Railtie class which inherits from
Rails::Railtie within your extension's namespace. This class must be
loaded during the Rails boot process.

The following example demonstrates an extension which can be used with or
without Rails.

Finally, you can also pass :before and :after as option to initializer, in
case you want to couple it with a specific step in the initialization
process.

Configuration

Inside the Railtie class, you can access a config object which contains
configuration shared by all railties and the application:

classMyRailtie<Rails::Railtie# Customize the ORM
config.app_generators.orm:my_railtie_orm# Add a to_prepare block which is executed once in production
# and before each request in development
config.to_preparedoMyRailtie.setup!endend

Loading rake tasks and generators

If your railtie has rake tasks, you can tell Rails to load them through the
method rake_tasks:

By default, Rails load generators from your load path. However, if you want
to place your generators at a different location, you can specify in your
Railtie a block which will load them during normal generators lookup:

Application, Plugin and Engine

A Rails::Engine is nothing more than a Railtie with some initializers
already set. And since Rails::Application and Rails::Plugin are engines,
the same configuration described here can be used in all three.

Be sure to look at the documentation of those specific classes for more
information.

# File 'railties/lib/rails/railtie.rb', line 181defload_tasks(app=self)extendRake::DSLifdefined?Rake::DSLself.class.rake_tasks.each{|block|block.call(app)}# load also tasks from all superclasses
klass=self.class.superclasswhileklass.respond_to?(:rake_tasks)klass.rake_tasks.each{|t|self.instance_exec(app,&t)}klass=klass.superclassendend